This invention relates generally to a method of construction, and more particularly relates to an improved system for joining highly durable panels to a rigid framework for use in an environment subject to a wide range of temperatures. Such a system is particularly well suited for joining polycarbonate panels to an aluminum framework in the construction of air cargo containers.
The manufacture of air cargo containers epitomizes the need for a method of construction that yields a strong and durable yet lightweight structure and one that can quickly and easily be repaired. Such containers have heretofore been typically constructed of aluminum. Aluminum sheet material riveted to an aluminum frame provides a relatively lightweight and strong structure. However, aluminum dents easily and the repair of such a structure calls for the labor intensive removal and subsequent replacement of all the fasteners with which the damaged panel is affixed to the frame. A unibody design of molded plastic material has been an alternative approach, although it suffers from shortcomings in its durability and repairability. A further reduction in weight of any such structure is a continually welcomed improvement.
The superior weight and strength characteristics of polycarbonates suggest that the use of such materials in the construction of air cargo containers would be a most advantageous adaptation. Affixation of polycarbonate panels to a rigid aluminum frame can provide a structure that is extremely light, strong and durable. An inherent disadvantage of such a construction is a direct result of the high coefficient of thermal expansion of the polycarbonate and more particularly, it is the large difference between the coefficient of thermal expansion of the polycarbonate relative and the coefficient of thermal expansion of the aluminum framework that causes difficulties. Conventional fastening means are ill-suited for interconnecting these two types of materials when they are to be cycled through wide temperature ranges. An air cargo container typically encounters temperatures from about -40.degree. F. to 160.degree. F., a range which imparts highly disproportionate amounts of dimensional changes to such a structure. Just a few cycles through such temperature extremes leads to fatigue and failure of a conventionally assembled polycarbonate and aluminum structure. Failures are typically manifested by hole fracture as the expanding and contracting panels repeatedly strain against the screws, bolts or rivets with which the panels are fastened to the rigid aluminum frame. In addition to the failure problems resulting from the affixation of such panels to the framework using conventional fastening means, replacement of damaged panels is a rather labor intensive operation.